Process for electrolytically removing iron-oxid scale.



CHARLES W. DANFOBTH AND NOBLE JONES, OI SHARON, PENNSYLVANIA.

PROCESS FOR ELECTBOLYTICALLY mOVINGIBON-OxID SCALE.

No Drawing.

Specification of Letters latent.

Application filed June '25, 1808. Serial No. 504,879.

Patented Nov. 9., 1009.

To all whom it "may concern:

Be it known that we, CHARLES \V. DAN- .ronrn and Nonnn Jones, citizens of the United States, residin at Sharon, in the county of Mercer an State of PennsvL Vania, have invented certain new and useful Improvements in Processes for Electrolytically Removin Iron-Oxid Scale, of which the following is a s ccification.

Many processes liave been proposed for removing it'on-oxid scale from the surface of iron and steel. Some by merely dipping the iron or steel in the ordinary picklebath which latter consists of acids, more or less concentrated. These, if the bath be concentrated so as to work rapidly, are prone to damage the iron or steel, while, if the bath is not so strong as to injure the material dipped, are exceedingly slow and tedious of operation. Scale may also be removed from iron and steel by means of the electric current, in acid, neutral and alkaline solutions, the action being somewhat similar, (though much more rapid and thorough) to the common method of pickling by immersion in acid solution. Direct or alternating current may be used, and alternating current appears to hasten the action of pickling over the ordinary method of dipping. Using a direct current and making the article to be cleansed the anode in an acid electrolyte, the material suffers loss along with the scale but the time required for complete pickling is much shortened. By using a dilute acid electrolyte and making the article to be cleansed the cathode, the mill-scale is reduced, and by a proper regulation of current. no steel proper is dissolved. This process, however, is not rapid enough for commercial purposes. \Vhen a strong solution of acid is used as the electrolyte, a strong current is necessary to protect the article from burning, which makes this process too expensive.

Various solutions have been suggested so that the steel would be rotected from the action of a strong acid ath Without the use of the electric current and Without increasing the length of time of immersion. Of the many proposed, the. most notable have been stannous chlorid, bisulfate salts and a mixture of acid and hydrocarbon oil. Stannous chlorid is too expensivefor practical use. The other two are efficient but reduce the speed of the operation.

The object of our invention is to over- I i l l come all these disadvantages and thus produce a flexible, rapid and economical method of removing iron-oxid scale.

By making use of a combination of the electric current in combination with a solution in water of a bisulfate of an alkaline metal, such as sodium or potassium, the roeess is made rapid and adaptable to all 0 asses of work and produces a better surface on iron and steel for subsequent operations, such as galvanizing, tinning, electroplating lacquering, enameling, japanning, etc., a this by a much more economical process as a much weaker electric current is required. This protection of the iron or steel by using a solution of a bisulfate salt as an electrolyte is due to the formation, for an instant, of a film of caustic alkali on thesnrface of the article to be cleansed by the decomposition of the alkaline bisulfate by the action of the electric current, which caustic alkali and free acid radical recombine to form the salt when removed from the sphere of immediate contact with the iron orsteel electrode. electrolytic method using only acid, the h drogen evolved is the only protection to tl ie iron or steel from the corrosive action of the strong acid. This necessitates the generation of much more hydrogen than is necessary for the reduction of the oxids in order that the steel be not attacked by the acid. In our process, both hydrogen and caustic alkali are formed on the steel cathode and since caustic alkali is not gaseous, it has a. greater protective efiect than gaseous hydrogen because it is not removed so rapidl- Hence very much less caustic alkali will more effective than the enormous amounts of hydrogen gas generated by the heavy current in the simple electrolytic method. With ten per cent. solution of a bisulfate salt, the strength of the electric current need be but from? to 10 amperes to generate sufiicient hydrogen to reduce the mill-scale and enough caustic alkali to protect the steel from burning and will remove common mill-scale in less than four minutes. The use of a stronger solution of bisulfate increases the rapidity of the process, with a corresponding increase of the electric current. The proportions to be used and the strength of the electric current depending on speed required. The temperature has a great influence on the speed of the process, but except in special cases it would not be economical to heat, above C.

The preferred method of procedure con- In the using suitable anodes whic will be unatfecte by the combined action of the electric current and electrolyte. By way of example, in a case where it is desired to eflect the cleanin of the iron orsteel article rapidly, the 0 lowing method is the pro er procedure.

Make a solution by weight. of a bisulfate of an alkaline metal in water at 20 C. Adjust the electric current at 50 amperes per. sq. ft., and the tem erature of the solution to between 40 an 60 C. As the operation proceeds and the free sulfuric acid is consumed, add oil of vitriol so that the free acid will not fall below 18%. When the solution becomes nearly saturated with iron sulfate, allow the temperature to rise to 75 C., and before deposition of salts beins, draw off the solution and allow to cool.

opperas (iron sulfate) will separate out but none of the alkaline metal salt will crystallize. The only loss of alkaline metal salt will be that adhering to the copperas crystals as mother-liquor Remove the crystals from the solution, and raise same to original acidity, and proceed as before.

Where a speed of about four minutes immersion of the article is sufiicient, a 10% solution of the bisulfate of an alkaline metal in water is efficient, usin a current of from 7 to 10 amperes per sq. t. y

'We are aware of the factv that bisulfate of soda has been used as a pickling bath and that a patent therefor was granted to A. K. Eaton of Brooklyn N. Y., June 10th, 1902, No. 702,050, and also that sulfuric acid in an electrolytic process has been used for removing scale and that patents therefor were ranted to Charles J. Reed of Philadelphia,

a., July 31st, 1906, No. 827,179 and No.

827,180 and June 4th, 1907, No. 855,667, but we are not aware of any process wherein bisulfate of soda is used as an electrolyte for electrolytically removing iron-oxid scale.

sire to secure by Letters Patent, is-

1. The process of electrolytically removing iron-oxid scale from the surface of iron and steel which consists in subjecting same as cathole to the action of an electric current, while submerged in a solution containing bisulfate of an alkaline metal in water.

2. The process of electrolytically removing iron-oxid scale from the surface of iron and steel which consists in subjecting same as cathode, to the action of an electric current, While submerged in a solution containing an acid sulfate.

3. The method of removing iron-oxid scale from the surface of iron or steel, which consists of passing an electric current of the proper density to same as cathode from an electrolyte containing a solution of a bisulfate of an alkaline metal at a temperature of not less than 40 C.

4. The process of removing iron-oxid scale electrolytically from the surface of iron and steel, which consists in )lacing same in a solution containing a bisu fate of an alkaline metal in water, and of passing to the metal as cathode an electric current of not less than 7 am eres per square foot.

Witness our hands t is 22nd day of J une, 1909.

CHARLES W. DANFORTH. NOBLE JONES.

In presence of- R03! NEVILLE, ANNA THoMAs. 

